I'm a fool. A moron. I failed to heed the warnings that the PPU had some solder points that needed tons of heat to work, and rather than be more careful, I got in a hurry. I tore up traces, and broke pins off of my PPU.

I have since gone through as carefully as I could and jumped all of the damaged traces I could find, and installed the dip socket that came with my NESRGB board - but I must admit that I am in over my head. I get a black screen when powering up - but if I use my multimeter to check the composite video signal, I get what amounts to 1Vpp, which if I understand it correctly, is a proper voltage for a composite video signal. I get black screen from composite video, svideo, and RGB.

I have installed the PPU into a second socket that it will permanently live in, dremeled part of the package itself away and soldered wires to the exposed copper to repair the chip as best as I could. I get 5v at the NESRGB board.

Here's a bunch of pictures of the disaster I have created. I am acting out of paranoia at this point checking continuity all over the place, using this pin map:

Right away I'm concerned, because I don't have continuity from pin 3/D1 on the PPU to pin 10/D0 on U1 (sram) - but I have bridged continuity D1 to D2 on SRAM, and D2 on the PPU has continuity to those two points - however no continuity D1 to D2 on the PPU itself. Very odd. :\

Halp. I can't tell if I have killed the PPU or not. I don't currently own an o-scope or logical analyzer, and from what I can tell a replacement PPU will run me $60. At that point I could almost afford to just buy a new one and start over.

What can I do here? Right now I'm just matching up pin names and testing continuity out. Finding things that leave me confused, like the PPU diagram I have shows pins 14, 15, 16, and 17 as R, G, B and I assume sync (it's black). Yet from my pictures, it looks as though 14 and 15 were bridged, and 15 and 16 were bridged, and all 4 have continuity to ground, so that's what I reproduced as best I could.

Finding things that leave me confused, like the PPU diagram I have shows pins 14, 15, 16, and 17 as R, G, B and I assume sync (it's black). Yet from my pictures, it looks as though 14 and 15 were bridged, and 15 and 16 were bridged, and all 4 have continuity to ground, so that's what I reproduced as best I could.

2C03 wasn't used in the NES or most Famicoms, but rather only in the Vs. System, Playchoice 10, and Famicom Titler.

In the 2C02, those four pins are instead a digital input/output bus that's used by the NESRGB to get the pixel values from the PPU.

Remember that you can use your computer's soundcard as a cheap oscilloscope. It's not great bandwidth (you'll probably only be able to sample at 48, 96, or 192kHz, and there's a strong lowpass filter at 10kHz) but it'll be enough to actually see if signals are high, low, or changing at slow-ish rates. (Just remember to add current limiting on the input).

numbski wrote:

Right away I'm concerned, because I don't have continuity from pin 3/D1 on the PPU to pin 10/D0 on U1 (sram) - but I have bridged continuity D1 to D2 on SRAM, and D2 on the PPU has continuity to those two points - however no continuity D1 to D2 on the PPU itself. Very odd. :\

D0 should be connected to D0, and D1 to D1, and D2 to D2 ... why are you looking for connectivity otherwise?

There's an easy way to check if the bond wire was not broken and there is connection between pin and internal chip core - set your multimeter to diodetest, touch + of your probe to GND and - to the pin you're testing. If multimeter shows some value (other than infinity), then it wil probably be the forward voltage of internal clamp diode and it means there is connection to the pin.

I tested in on UA6538 and all pins could be tested that way.

Of course there might be other damage to internal structure due to heat.

Finding things that leave me confused, like the PPU diagram I have shows pins 14, 15, 16, and 17 as R, G, B and I assume sync (it's black). Yet from my pictures, it looks as though 14 and 15 were bridged, and 15 and 16 were bridged, and all 4 have continuity to ground, so that's what I reproduced as best I could.

2C03 wasn't used in the NES or most Famicoms, but rather only in the Vs. System, Playchoice 10, and Famicom Titler.

In the 2C02, those four pins are instead a digital input/output bus that's used by the NESRGB to get the pixel values from the PPU.

Remember that you can use your computer's soundcard as a cheap oscilloscope. It's not great bandwidth (you'll probably only be able to sample at 48, 96, or 192kHz, and there's a strong lowpass filter at 10kHz) but it'll be enough to actually see if signals are high, low, or changing at slow-ish rates. (Just remember to add current limiting on the input).

numbski wrote:

Right away I'm concerned, because I don't have continuity from pin 3/D1 on the PPU to pin 10/D0 on U1 (sram) - but I have bridged continuity D1 to D2 on SRAM, and D2 on the PPU has continuity to those two points - however no continuity D1 to D2 on the PPU itself. Very odd. :\

D0 should be connected to D0, and D1 to D1, and D2 to D2 ... why are you looking for connectivity otherwise?

The NES is basically "W"RAM <-> CPU <-> PPU <-> "V"RAM. When you're testing continuity, are you testing the correct side of the PPU for the RAM you're testing against?

I was testing D1 to D1, and my probe slipped on U1 making contact with the next pin. I didn't do it on purpose, but after I saw I had continuity that didn't seem like it should be there, I got curious.

re: using my sound input as an oscilloscope, everything I am finding is for windows. I'm a Linux and Mac user - so I either need to get that software running under wine, or I will have to play some games to get it going under a VM. That's still more than I was aware of before, so I super appreciate that!

Now I just need a logical analyzer.

EDIT - never mind, I have a bus pirate from an old project that apparently can be used as a logic analyzer!

Might need some help, I was playing with it last night and the current Debian packaging didn't enable sound card input (oops) ... and the current build only allows sample rate of 44.1kHz and lower right now (double-oops)

There's an easy way to check if the bond wire was not broken and there is connection between pin and internal chip core - set your multimeter to diodetest, touch + of your probe to GND and - to the pin you're testing. If multimeter shows some value (other than infinity), then it wil probably be the forward voltage of internal clamp diode and it means there is connection to the pin.

Interesting...I've tried this on a MMC3 clone named 9112 that seems dead, and have found many pins to have infinite resistence and a short circuit in the M2 and GND.

Seems that it's death is finally confirmed. I just would like to know why.Have I messed very badly with the IC and end killing it?I could not read anything other than FFs from this game ROMs too, so, maybe it was already dead when I got it.But again, what can cause this kind of failure on a cartridge? Static eletricity? A ray storm?Sorry to go off-topic...

There's an easy way to check if the bond wire was not broken and there is connection between pin and internal chip core - set your multimeter to diodetest, touch + of your probe to GND and - to the pin you're testing. If multimeter shows some value (other than infinity), then it wil probably be the forward voltage of internal clamp diode and it means there is connection to the pin.

I tested in on UA6538 and all pins could be tested that way.

Of course there might be other damage to internal structure due to heat.

Your picture shows you doing this with the chip unsocketed. I assume I must do the same. Working on this now. Been really sick. :\

I did your diodetest - but before that, I learned quite a bit about repairing IC legs. :\

The way that worked best for me was to get ahold of a zif socket for the ic, and then one leg at a time insert a spare LED or cap leg into the missing leg section, apply some no-clean flux, and then apply solder to the iron and touch the iron to the new leg for 2-3 seconds until I got a bond.

While I was as it, I tinned the rest of the legs (2 seconds of the iron, max) so that those legs had a little reinforcement.

Given this is my first time fixing up an IC, it didn't turn out terribly...

After moving the ic from the zif socket to another socket that will fit the NESRGB, I tested all of the legs with my diodetest as you described, and forward voltage registered on all of them. Looking through the rest of the suggestions to figure out how to proceed, because after I put the chip back into the NESRGB, and then installed it into my top loader, I still get a black screen - tested composite, svideo, and rgb. Same results across the board.

I'm part of the way through this process, but I get stuck going from the "V"RAM at U4 to the PPU. I'm looking at the block diagram, and I'm getting a little sidetracked. Here's what I've sorted out so far:

Starting to make a little more sense out of the block diagram. I think.

PPU pin 25 should have continuity to pin 37 on the cartridge connector, right?

Wanted to sanity check myself, because I seem to be missing a whole lot of connectivity. According to this block diagram, I should have a direct connection from PPU pin 29 and U2 pin 1, but I have nothing.

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